Field of the Invention
The present invention relates to toners used in imaging methods of forming electrophotographic images or electrostatically charged images into apparent images, and imaging methods.
Description of the Related Art
Electrophotographic systems apply an electrostatic force or pressure to toner images developed on photosensitive members to transfer the toner images onto paper media. The toners used in such electrophotographic systems should have one important performance, i.e., transfer properties. Imperfect transfer of images result in image defects such as no or insufficient deposition of the toners. Accordingly, toners having high transfer properties are required to attain high quality images. Methods of preparing spherical toners to enhance transfer properties are proposed, and examples thereof include a method of preparing a toner having a circularity of 0.92 or more and less than 0.95 (Japanese Patent Application Laid-Open No. 2007-58134), and a method of preparing a toner having a circularity of 0.95 or more (Japanese Patent Application Laid-Open No. H11-295931).
Unfortunately, toners having high circularities readily roll on the surfaces of photosensitive members. Non-transferred toner T readily intrudes into the contact region N, as illustrated in FIG. 1, between a photosensitive member 310 and a cleaning blade 308, and readily escapes from the cleaning region through the contact region N.
In the conventional configurations, the contact pressure of the cleaning blade pressed against the photosensitive drum is increased to prevent such intrusion of the spherical toner into the cleaning nip, attaining favorable cleaning. However, higher contact pressure of the cleaning blade increases a load on a blade edge under environments at low temperature, high process speed, and high rotational speed of the photosensitive drum. Such an increase in the load on the blade edge may cause another problem after long-term use, such as partially chipped cleaning blades. For this reason, examination of spherical toners having high cleaning properties at low contact pressure of the cleaning blade is required.
Japanese Patent Application Laid-Open No. 2002-318467 proposes a method of form a layer of an external additive having a large particle diameter to block a toner particle. This disclose uses a toner including a combination of an external additive having a large particle diameter (such as sol gel silica) having a spherical shape and a sharp particle diameter distribution with an organic compound having a smaller particle diameter. It is confirmed that a toner having such a configuration has enhanced cleaning performance whereas it has been found that the toner escapes from the cleaning blade at a higher process speed.
Japanese Patent Application Laid-Open No. 2012-68325 proposes a method of preparing a toner having an adhesive force reduced by an external additive embedded into the surface of the toner to reduce an untransferred toner and enhance cleaning properties. It has been confirmed that the toner having such a configuration has enhanced cleaning performance whereas it has been found that the toner may escape from the cleaning blade during image formation under environments at low temperature and a higher process speed.